The present invention relates to a method of preventing the corrosion of metallic wirings for LSIs or the like formed on the surface of a substrate.
As the material of metallic wirings for LSIs or the like, there may be used a single-layer film comprising aluminium., refractory metal (titanium, titanium nitride, tungusten, titanium tungusten) or an aluminium alloy (containing about 1% of silicon and about 0.5% of copper), or a multi-layer film comprising an aluminium alloy and refractory metal.
Such metallic wirings are formed by etching a metallic film formed on a silicon oxide, for example, a metallic film containing aluminium, with chlorine-containing gas such as BCl.sub.3, SiCl.sub.4, Cl.sub.2 or CHCl.sub.3. The reason why the chlorine-containing gas is used, is because an aluminium chloride (AlCl.sub.3) which is a compound of aluminium and chlorine, presents the highest vapor pressure among compounds of aluminium with fluorine, chlorine, bromine, iodine or the like.
FIGS. 7 (a) to (c) show conventional dry-etching steps with an aluminium alloy used as the material of metallic wirings.
As shown in FIG. 7 (a), a silicon oxide film containing boron and phosphorus (hereinafter referred to as BPSG film) 2 is formed on a substrate 1, an aluminium alloy film 3 is then formed on the BPSG film 2 and photoresists 4 are then formed on the aluminium alloy film 3. More specifically, the BPSG film 2 is deposited by a thickness of 700 nm on the substrate 1 by a chemical vapor deposition method (hereinafter referred to as CVD method). Then, there is deposited, by a thickness of 800 nm, the aluminium alloy film 3 comprising an aluminium alloy containing 1% of silicon and 0.5% of copper (hereinafter referred to as Al-Si(1%)-Cu(0.5%)) by a sputtering method. Applied to the aluminium alloy film 3 is a resist film, which is then subjected to photolithography to form the photoresists 4 in a desired pattern.
As shown in FIG. 7 (b), with the photoresists 4 serving as masks, the aluminium alloy film 3 is etched by a reactive ion etching method with the use of chlorine-containing gas such as SiCl.sub.4, Cl.sub.2, CHCl.sub.3 or the like, thus forming aluminium alloy wirings 5 in a desired pattern. At this time, a great amount of chlorine-containing substances 6 comprising residual chlorine and a chloride such as AlCl.sub.3 and the like, sticks to the lateral walls of the photoresists 4 and the aluminium alloy wirings 5. If the substrate 1 is taken out in the air with no surface treatment applied to the aluminium alloy wirings 5 after completion of the etching, there is a likelihood that the chlorine-containing substances 6 sticking to the photoresists 4 and the aluminium alloy wirings 5 are reacted with water content in the air to cause the aluminium alloy wirings 5 to be corroded. Such corrosion may result in serious troubles such as disconnection of the aluminium alloy wirings and decreased reliability of the semiconductor devices.
In a conventional method, upon completion of the etching of the aluminium alloy film 3, the substrate 1 has been conveyed into another chamber without the aluminium alloy wirings 5 exposed to the air. After the photoresists 4 to which a great amount of residual chlorine and a chloride sticks, and major portions of the chlorine-containing substances 6 sticking to the lateral walls of the aluminium alloy wirings 5, had been removed by oxygen plasma in the chamber above-mentioned, the substrate 1 has been taken out in the air, as shown in FIG. 7 (c).
In the method using the oxygen plasma above-mentioned, however, the corrosion of the aluminium alloy wirings has not been perfectly prevented. More specifically, according to the method using the oxygen plasma, the photoresists 4 and a major portion of the chlorine-containing substance 6 sticking to the surface of the substrate 1 have been removed, but chlorine atoms entered in the grain boundary of the aluminium alloy wirings 5 could not been removed and have reacted with water content in the air.